An Example of the Use of Money as a Medium

An example of the use of money as a medium of exchange is:

A) Mike gets a friend to give him a beer today in return for promising to give the friend two beer when Mike gets paid at the end of the month.
B) Judy lends her car to a friend who signs a promissory note that she will pay Judy $10 a day for the use of the car after she returns the car to Judy.
C) ABC Investments Inc. enters in its account books that it owes Nallai $20 for his last month's investment income.
D) Dave keeps $250 in his drawer for a 'rainy day'.
E) Barry pays $275 with his bank debit card for tickets for an NHL play- off game.